John Bruton, who was taoiseach in Ireland from 1994 until 1997, has died aged 76.
In a family statement, it was announced that he "died peacefully in the Mater Private Hospital in Dublin, surrounded by his loving family, early this morning following a long illness".
"He was a good husband, a good father and a true patriot," the statement added.
Mr Bruton was leader of Fine Gael from 1990 until January 2001.
As taoiseach he was instrumental in working with British prime minister Sir John Major to launch the Anglo-Irish Framework Document in 1995, which proposed new relations between Ireland, Northern Ireland and the UK.
In 2002 he was re-elected to the Dail - the lower house of the Irish parliament - until he resigned his seat two years later.
He was then appointed the EU Ambassador to the United States, which he did until 2009.
Leading the tributes, Sir John said: "I was shocked to learn of the loss of John Bruton.
"He was a brave and talented taoiseach who contributed mightily to the early days of the peace process.
"In testing circumstances, he put peace above political self-interest to progress the path towards the end of violence.
"He was a formidable servant of the Irish nation and of peace, and I am deeply saddened at his passing."
'Deeply committed politician'
Taoiseach Leo Varadkar said he was "devastated" to learn of Mr Bruton's death, adding that he was "one of the reasons I became involved in politics and joined Fine Gael".
"We kept in touch and his knowledge and experience were particularly helpful during Brexit and during coalition negotiations," the taoiseach said in a statement.
Praising his work as vice president of the European People's Party and opposing violence, Mr Varadkar said: "I believe John Bruton possessed real dignity and imbued compassion and patriotism.
"The whole Fine Gael family mourns his loss, and he will always be remembered for his service to our Party and to the Irish State."
President of Ireland Michael D Higgins added that Mr Bruton was a "deeply committed politician, who demonstrated a life-long interest and engagement in public affairs and public service both in Ireland and internationally".
"Always bristling with ideas, and occasionally demonstrating an impatience with the difficulties of implementation, those of us who worked with John, be it in government or in opposition, will recall the energy which he brought to the different parts of politics," Mr Higgins said.
"This continued in John's many contributions to the public debate in the years following his departure from office and, in all of his roles, was something which I always very much welcomed and found very refreshing."
Jeffrey Donaldson, leader of the Democratic Unionist Party, referred to Mr Bruton as a "gentlemen" who, as prime minister, "reached out to unionists to try and gain a better understanding of our position and to encourage practical cooperation".
"Our thoughts and prayers are with his family at this time," he wrote on X.
Northern Ireland First Minister Michelle O'Neill also sent condolences to Mr Bruton's family while speaking in the Assembly.
"I want to pass on my condolences to the family of former taoiseach John Bruton, who we've just been notified has sadly passed away," she said.
"To his family and friends, we send them our condolences at this very sad time."
The family statement said that Mr Bruton is survived by his wife, Finola, son Matthew and daughters; Juliana, Emily and Mary-Elizabeth, grandchildren, sons-in-law, his brother, Richard and sister, Mary, nieces, nephews, many cousins and extended family.